This study is a clinical trial to determine the safety and efficacy of cysteamine in the treatment of nephropathic cystinosis, a metabolic disease which usually leads to end-stage renal disease before 10 years of age. All children enrolled in the trial will receive cysteamine. Control information is provided by data collected on 30 patients who were randomized to placebo in a previous trial evaluating the efficacy of Vitamin C for the treatment of this disease. Approximately 90 children will eventually be enrolled in the current trial, which is anticipated to last about one more year. Evaluation of the drug's effectiveness will be chiefly determined by the creatinine clearance values of the treated children as compared with those of the historical controls.